This invention relates to improvements in a method of driving a thermal printing head, and more particularly to a method of thermally controlling a thermal printing head so as to enable the head to effect high speed recording.
Since thermal recording systems can reproduce picture images simply by means of thermal energy, they are useful as simple recording systems and the range of their use is rapidly increasing. For example, such recording systems are widely used in facsimile equipment and the like.
The conventional thermal recording systems have comprised a thermal printing head including a plurality of heat generating resistors disposed in a row, and a transistor connected between each of the heat generating resistors and an associated one of a plurality of signal terminals to which picture signals are applied respectively. The transistors are responsive to associated picture signals for being put in their ON states thereby to permit a current from a common source terminal to flow into those heat generating resistors connected to the conducting transistors to generate Joule heat. The resistors thus heated from elemental picture images or dots on a section of thermally sensitive paper contacted by the resistors as determined by the picture signals. This process is repeated with successive rows of the section of thermally sensitive paper to form a received picture image on the section of paper.
However, during repetition of the process as described above, the temperature of the heat generating resistors slowly rises due to the residual heat effect caused from the preceding flows of current through the resistors resulting in blurring of the recorded dots. Alternatively, the thermal printing head might be broken. Further the conduction-of-current cycle for each row on the thermally sensitive paper has been unable to be shortened beyond a particular limit because time intervals are required for heating and cooling the heat generating resistors.
Accordingly it is an object of the present invention to provide a new and improved method of thermally controlling a thermal printing head so as to increase the recording speed required for facsimile equipment and the like.
It is another object of the present invention to provide a new and improved method of thermally controlling a thermal printing head so as to improve the quality of pictures recorded by facsimile equipment and the like.
It is still another object of the present invention to provide a new and improved method of thermally controlling a thermal printing head so as to decrease a driving power required for recording by facsimile technique and the like.